Frequency generators

ABSTRACT

A frequency generator produces a comb-like spectrum of frequencies, each of the frequencies being derived from a single standard frequency. A relatively small number of predetermined frequencies are derived directly from the standard frequency and arranged in groups. Thereafter all frequencies in each group are mixed with all frequencies in all other groups to produce the required comb-like frequency spectrum. The invention permits a large number of frequencies to be accurately derived from a single frequency in a practicable and economical manner.

United States Patent 1191 Miller A [45] July 30, 1974 FREQUENCY GENERATORS 3,069,631 12/1962 Adams 331/38 x Inventor: William Francis Miller chelmsford 3,119,078 1/1964 Stone, Jr 331/38 England Primary Examiner-Ronald'L. Wibert [73] Assignee: The Marconi Company Limited, Assistant Examiner-Richard A. Rosenberger Chelmsford, Essex, England Attorney, Agent, or FirmBa1dwin, Wight &' Brown [22] Filed: Oct. 30, 1972 [5 7] ABSTRACT A frequency generator produces a comb-like spectrum of frequencies, each of the frequencies being derived Foreign Application Priority Data from a single standard frequency. A relatively small 061. 28. 1971 Great Britain 50107/71 u ber of predetermined frequencies are derived di- 1 I rectly from the standard frequency and arranged in [52] US. Cl. 331/38, 331/43 g p e ea te all requencies in each group are [51] Int. Cl. H03b 21/02 mi wi h all frequencies in all other groups to pro- [58] Field of Search 331/38, 40, 43, 39 duce he required comb-like frequency spectrum. The invention permits a large number of frequencies to be [56] Ref rence Cit d accurately derived from a single frequency in a practi- UNITED STATES PATENTS cable and economical manner. 2.445.664 7/1948 Doelz 33l/38 6 Claims, 6 Drawing Figures 70 MHz 1 Hz 50 MHz g g 3M POWER osa g 706MHz 1 50 MHz 50 MHz 8) g POWER 050. 6 04 v 9: 1: MHz 38- 39 40 745+ 10/ 4/42 50/4/12 SOMHZ a; Q? g 7 POWER 0$C.- 43 MHZ o P 39 39 4o 9a Q MHZ x 49%!14 42 49%MH2 Q5) POWER 050. WP

9/ MHz MHz 49 MHz (2g) 8 3 '4" 496 POWER osc. 9o O/P MHZ 4OMHZ improvements FREQUENCY GENERATORS This invention relates to frequency generators and 1 more specifically to frequency generators which pro duce a comb-like spectrum of frequencies. It is becoming increasingly necessaryto'provide frequency generators which produce simultaneously a large number of iquency having a precisely predetermined value. The

diffcultiesin produc'ing a comb-like frequency specgenerating acomb like spectrum of frequencies -in-'- cludesmeans for generating a plurality of different .a pair of channels'providing outputs'having adjacent frequency values is coupled to a mixer,this mixer being arranged to provide adifference frequency equal to'the 7 difference in" frequencies applied to it, and said differfrequencies, for example, 'a hundred or more, each fregroups of frequencies,.eachi group containing a plurality. "of different frequencies', and means for mixing all frequencies" in each 'gro'up"1of frequenciesfwith all frequencies in all 'other -groups of frequencies'to produce a plurality of frequencies which together constitute the comb-like spectrum of frequencies andwhich are equal in number totheprodufctof the numbers of frequencies in e'achofsaid groups of frequencies whichare so mixe I is usual, for practical reasons, to mix onlytwo frequencies-together in'any one individual mixer, and

preferably each mixer. is'previded witha frequencyselec'tive filterwhich eliminates unwantedharmonics. Where only two frequencies are mixedtogether in any one mixer preferably the frequency-produced as. a result of mixing together two frequeneies from two different groups is mixed withone frequency from yet another group, andtheresulting frequency mixed .with another frequency from. yet another group until a frequencyfrom all groups'has-been mixedin' thiswayfi Whereit is necessary to providea coherent phase relationship between all; frequencies in the comb-like spectrumof frequencies, all frequencies in all the different groups of frequencies are .preferably derived from a single source of frequency. Preferably again this single source of frequency is a stable crystal controlled oscillator.

In one embodiment in accordance with this invention each of the frequencies'in the comb-like spectrum of frequencies is synthesized'in a different frequency synthesizing channel, each channel including in a serial path, a first mixer followed by a first band-pass filter, and a plurality of second mixers each followed by a band-pass filter, the number of second mixers being equal to the number of said different groups of frequencles. r

' Preferably a controllable-gain amplifier is present in the said path between the said first pass-band filter and the plurality ofsecond mixers. Preferably again the amplitude of an output frequency resulting from the said plurality of second mixers is compared-with an amplitude reference signal and the gain of the controllablegain amplifier controlled in dependence on the result of this comparison to provide an output frequency having a desired amplitude.

Preferably there is present in an input path of the first mixer a controllable phase shifter, which is controlled in dependence onthe phase of the output frequency.

Preferably again the said channels] are arranged to produce a comb-like spectrum of frequencies in which the'frequencies are regularly spaced; the frequency difstepsof one-third MHzJ ence frequency being applied to a further mixer to which is also applied a reference frequency equal. to the nominalvalue of the-difference, frequency, said further mixer being arranged to providean output signal representative-of the phase .difierence between the two frequencies applied to it, and said representative signal being usedto control the said controllable phase shifter soa's to reduce the said. phase difference. The invention will befurther described, by way of example,'with reference tothe'accornpanying drawings in FIG. lshows in diagrammatic form the generation of a single ot'rtp'utfrequency, I v FIG. 2 shows in diagrammaticform the generation of a numberof output frequencies,- '7 7 f R38. 3, and 5 show in diagrammatic for m generation of certainfrequencies foruse in connection w h IGS-1 a l nd. i FIG.6showsinidiagrammatic orm the generation-bf certain frequencies for use 'n connection with FIGS. 3 m, 'f

The drawings illustrate the generation of a regular comb-like frequency spectrum having l 25 discrete freg quencies extending from 49%Ml-lz to 90% MHz in Referring to FIG. l'there is showntherein a single frequency synthesizing channel. The complete fre-. quency generator includes 125 such channels, one for eachoutput frequency. A f xedfreque'ncyjof '80 MHz is'ap'plied via a terminal 1 'to'a'firstmixerlito which is also appliedjvia a terminal 3 and a controllable phase shifter4 a fixed frequency of MHz. The two frequencies are mixed in the mixer land the resultant is passed through a narrow bandfilter 5 which passes only the difference frequency of 20 MHz. The frequency of 201MHz is passed'via a controllable-gain amplifier 6 to a further mixer7 where it is mixed with a frequency appliedto'a'terminal 8-, The frequency applied to the terminal 8-could have one of five values, ie., 49% MHz, 49% MHZ, SOMl-lz, 50% MHz or 50% MHz. These frequencies are termed herein Group 1 frequencies.

Output from mixer 7 is passed via a filter. 9 to a further mixer 10 where it is mixed with one of five frequencies which constitute Group ll frequencies. The

output of mixer 10 is passed via a filter 11. to a final MHz and2l 6% MHz. Output from mixer 12is passed viaa filter 15, an amplifier l6, and a coupler 17 to an output terminal 18. The coupler 17 is connected to a mixer l9'and one input of a comparator 20. Tenninal 21 is also connected to themixer l9, and in operation terminal 23 with a frequencylof one-third MHz. The

output of the mixer 22 is connected to control the controllable phase shifter 4. Comparator 20 is also fed with a d.c. reference voltage applied via a terminal 24 and the output of the comparator 20 is used to control the gain of the amplifier 6.

As already stated, there are provided 125 channels each like the channel shown in FIG. 1. For each channel, terminal 8 is connected to one of the five Group I frequencies, terminal 13 is connected to one of the five Group II frequencies, and terminal 14 is connected to one of the five Group Ill frequencies. To consider a specific case it is assumed that frequencies of 50 MHz, I MHZ and 200 MHz are applied to terminals 8, 13 and 14 respectively, and that filters 5, 9, 11 and 15 are narrow band pass filters and are arranged to pass frequencies of 20 MHz, 30 MHz, 130 MHz and 70 MHz respectively.

It will thus be apparent that the various mixing and filter stages produce an output of 70 MHz. This output is coupled to the mixer 19 where it is mixed with the output from an adjacent channel (which provides an output frequency of either 69% MHz or 70% MHz) to provide a difference frequency of one-third MHZ which is fed to mixer 22. Mixer 22 is fed, via terminal 23, with the reference frequency equal to one-third MHz, and as a result a d.c. signal is produced, which is used to control the controllable phase shifter 4 to bring the output of mixer 19 into exact phase with its MHz reference frequency.

In order to control the output amplitude, the output signal is coupled via the coupler 17 to the comparator 20 where it is compared with a reference signal applied via the terminal 24. In practice the reference signal could be a d.c. voltage level, and in this case the coupled output signal would be smoothed prior to comparison.

Referring now to FIG. 2, there is shown therein five channels of the kind shown in FIG. 1, like parts having the same references as in FIG. 1, and the channels being referenced 31 to 35. For the sake of clarity the phase, and amplitude control circuits have been omitted from this drawing. All channels are fed with the 80 MHz and the 60 MHz frequencies which are mixed in mixer 2. In the five channels shown the Group II frequency of 100MHz is unchanged and the Group III frequency of 200 MHz is unchanged, and each of the five Group I frequencies (50% MHz, 50% MHz, 50 MHz, 49% MHz and 49% MHz) is applied to channels '31 to 35 respectively to produce the five output frequencies 69% MHz 69% MHz, 70 MHz, 70% MHz and 70% M Hz respectively. In the complete frequency generator under consideration there are 125 different channels, each producing a different one of the frequencies in the comb-like frequency spectrum referred to previously. The total number of different frequencies obtainable is the multiple of the different frequencies in the three groups I, II and Ill, i.e., X 5 X 5 125. It will thus be appreciated that the 125 frequencies have been obtained from only frequencies. The frequencies of 80 MHZ and 60 MHz are merely carriers and could be dispensed with if desired, although the use of the 60 MHz frequency provides a particularly convenient way of controlling the phase of the output frequencies. It will be realised that if, say, four groups of five frequencies were used then the frequencies would be mixed to produce 625 different output frequencies.

In order that all of the output frequencies may be made phase coherent all of the frequencies are derived ultimately from a single 10 MHz crystal oscillator. The generation of the frequencies in groups I, II and III is shown in FIGS. 3, 4 and 5 respectively. In FIG. 3 a frequency of onethird MHz is applied to terminal 36 and a frequency of two-thirds MHz is applied to terminal 37. These frequencies are mixed with a 10 MHz frequency in mixers 38 which also include a filter tuned to the required mixed frequency to eliminate unwanted harmonics. The frequencies produced as a result of this mixing are passed to mixers 39 where they are mixed with a frequency of 40 MHz. After filtering the frequencies are passed to power oscillators 40. The frequencies obtained are clearly indicated on the drawing.

FIGS. 4 and 5 show in similar fashion the way in which the Group II and Group III frequencies are derived respectively. The operation of these circuits is analogous to that of FIG. 3 and it is not thought necessary to describe them in detail.

Referring to FIG. 6 there is shown therein the way in which all of the required frequencies are derived from a single 10 MHz crystal oscillator 61. Oscillator 61 feeds a series of frequency multipliers 62 each having a multiplication factor of two and each including a narrow band filter to remove unwanted harmonics. From these multipliers the frequencies of 20 MHz, 40 MHz, MHz and MHz are obtained. The oscillator 61 also feeds a divide-by-three frequency divider 63 which in turn feeds a divide-by-two frequency divider 64 from which the frequency of 1% MHz is obtained. The frequency of 3% MHz obtained from frequency divider 63 is fed both to a mixer 65, where it is mixed with the 20 MHz frequency obtained from frequency multiplier 62 to obtain a frequency of 16% MHz, and to a divide-byfive frequency divider 66 whichprovides the-frequency of two-thirds Ml-Iz. This frequency is passed through divide-by-two frequency divider 67 to obtain the frequency of one-third MHz. The frequency of 8 /3 MHZ is obtained by mixing the frequencies of 1% MHZ and 10 MHz in mixer 68 which incorporates a suitable filter.

I claim:

1. A frequency generator system for simultaneously producing a large number of output signals each of a different frequency and cumulatively defining a comblike spectrum of frequencies, comprising in combinatron:

means for generating a first group of different frequencies and including a stable oscillator;

means for generating from said first group of frequencies a plurality of further groups of different frequencies, the sum of said frequencies of said first and said further groups of frequencies being small in relation to said large number of output signals;

a plurality of mixing channels each including a first mixer and a plurality of serially connected second mixers, said first mixer of each channel being connected to a pair of frequencies of said first group and said second mixers of each channel being connected to a set of frequencies where each set comprises frequencies selected from each further group; and

and of said frequencies being related to produce said comb-like spectrum of frequencies from said mixing channels in which the number of frequencies in controlled in dependence on the phase of such mixing channel relative to a reference signal from the first group of frequencies.

2. A generator as claimed in claim 1 wherein each first mixer is followed by a first band-pass filter, and said second mixers are each followed by a band-pass filter, the number of second mixers being equal to the number of said different groups of frequencies.

3. A generator as claimed in claim 1 wherein a controllable-gain amplifier is present in the said path between the said first pass-band filter and theplurality of second mixers.

4. A generator-as claimed in claim 3 wherein the amplitude of an output; frequency resulting from the said plurality of second mixers iscompared with an amplitude reference signal and the gain of the controllablegain amplifier controlled in dependence on the result of this comparison to provide an output frequency having a desired amplitude.

5. A generator as claimed in claim 1 wherein the said channels are arranged to produce a comb-like specvide a difference frequency equal to the difference in frequencies applied to it, and said difierencefrequency being applied to a further mixer to which is also applied a reference frequency equal to the nominal value of the difference frequency, said further mixer being arranged to provide an output signal representative of the phase difference between the two frequencies applied to it,

and said representative signal being used to control the said controllable phase shifter so as to reducethe said phase difference. 

1. A frequency generator system for simultaneously producing a large number of output signals each of a different frequency and cumulatively defining a comb-like spectrum of frequencies, comprising in combination: means for generating a first group of different frequencies and including a stable oscillator; means for generating from said first group of frequencies a plurality of further groups of different frequencies, the sum of said frequencies of said first and said further groups of frequencies being small in relation to said large number of output signals; a plurality of mixing channels each including a first mixer and a plurality of serially connected second mixers, said first mixer of each channel being connected to a pair of frequencies of said first group and said second mixers of each channel being connected to a set of frequencies where each set comprises frequencies selected from each further group; and and of said frequencies being related to produce said comb-like spectrum of frequencies from said mixing channels in which the number of frequencies in said spectrum is large compared to said sum of frequencies; each mixing channel also including a controllable phase shifter in an input path of the first mixer and controlled in dependence on the phase of such mixing channel relative to a reference signal from the first group of frequencies.
 2. A generator as claimed in claim 1 wherein each first mixer is followed by a first band-pass filter, and said second mixers are each followed by a band-pass filter, the number of second mixers being equal to the number of said different groups of frequencies.
 3. A generator as claimed in claim 1 wherein a controllable-gain amplifier is present in the said path between the said first pass-band filter and the plurality of second mixers.
 4. A generator as claimed in claim 3 wherein the amplitude of an output frequency resulting from the said plurality of second mixers is compared with an amplitude reference signal and the gain of the controllable-gain amplifier controlled in dependence on the result of this comparison to provide an output frequency having a desired amplitude.
 5. A generator as claimed in claim 1 wherein the said channels are arranged to produce a comb-like spectrum of frequencies in which the frequencies are regularly spaced; the frequency difference between all pairs of adjacent frequency values being the same.
 6. A generator as claimed in claim 5 wherein the frequency output of each channel in a pair of channels providing outputs having adjacent frequency values is coupled to a mixer, this mixer being arranged to provide a difference frequency equal to the difference in frequencies applied to it, and said difference frequency being applied to a further mixer to which is also applied a reference frequency equal to the nominal value of the difference frequency, said further mixer being arranged to provide an output signal representative of the phase difference between the two frequencies applied to it, and said representative signal being used to control the said controllable phase shifter so as to reduce the said phase difference. 